The present invention relates to a supporting sheath for a longitudinally shirred packaging tube, to a functional unit comprised of the supporting sheath and the packaging tube contained therein and to a process for its preparation.
Meat products in the form of sausage emulsions filled into synthetic sausage casings are marketed in large quantities. Particularly preferred materials for the synthetic sausage casings are fiber-reinforced cellulose hydrate, collagen, or synthetic polymers such as, for example, polyesters or polyamides.
In the production of sausages, one begins with tubular pieces of a predetermined length, for example, of approximately 20 m. These tubular pieces are gathered in a known manner by means of conventional devices, for example, with tight pleating, into cylindrical, hollow sticks or rods open on both ends and are subsequently or during the process compressed axially in the direction of their longitudinal axis. This is known as shirring. Following the gathering of a tubular piece of the above-mentioned length, the self-supporting hollow stick or rod formed in this manner has a length of approximately 40 cm.
When the packaging tube forming the hollow stick is to be filled with sausage emulsion, it is first closed at one of its ends and then the hollow stick is, with its open end forward, pushed onto the stuffing horn of a sausage filling machine. The sausage emulsion is then continuously and under pressure filled into the hollow stick, which is thereby unfolded according to the amount of sausage emulsion pressed into the tube.
The hollow sticks or rods used possess a certain inherent rigidity provided by the manufacturing process, but they are sensitive to bending stress and easily break into two or more pieces, which are linked together by unfolded tubular pieces. The gathered tube forming the hollow stick is exposed to strong mechanical stresses during the filling process. For this reason, hollow sticks consisting of gathered tubular pieces of cellulose hydrate, are moistened prior to filling, in order to make them flexible.
As a result of the absorption of water by the tube and the subsequent swelling, there is the danger of an undesirable longitudinal expansion of the hollow stick and of damage to the stick during subsequent handling.
The danger that the hollow stick may lose its original shape and dimension because of the above-mentioned effect is particularly great when the tube forming the hollow stick has a relatively thick wall, for example, having a thickness of 0.07 mm, and has a relatively large internal diameter, for example, of 40 mm.
In DE-OS No. 25 10 637 a functional unit of the general type mentioned above is described. However, the extensions of the casing forming the turned-back portions have no elements preventing the subsequent independent return of the turned-back portions to their original shape. There is therefore the risk of the uncontrollable, at least partial returning of the turned-back portions to their original shape, together with an undesirable loosening of the seat of the supporting sheath on or around the hollow stick, so that the supporting sheath is no longer capable of adequately performing its function in relation to the fixation of the shape and dimensions of the hollow stick, particularly in the case of moistened hollow sticks.